As video compression schemes, MPEG (Moving Picture Experts Group), H.264/MPEG-4 Part 10 (Advanced Video Coding, hereinafter referred to as “AVC”), and HEVC (High Efficiency Video Coding) have been widely used.
In a case of special reproduction such as thumbnail reproduction or N-speed fast-forward reproduction (where N is not necessarily an integer) using such a compression scheme, a subsampling process is performed by decoding AUs (Access Units) and then selecting pictures to be displayed.
Since the AUs to be subsampled are determined after reordering the AUs into a display order after decoding, it has been difficult to discriminate whether each AU is to be subsampled before decoding. Furthermore, in a case in which an AU to be decoded is the AU referred to during subsequent decoding, it is always necessary to decode the AU for preventing artifacts.
Generally, since a decoding order differs from a display order, it is difficult to confirm whether or not an AU is to be subsampled at a time of decoding; thus, by not decoding AUs that are not referred to only in a case in which this reference cycle matches a subsampling cycle, the AUs can be subsampled before decoding.
On the other hand, in a case in which the reference picture cycle differs from the subsampling cycle, it is necessary to confirm the display order and then subsample the AUs by performing certain computation after decoding syntax necessary to confirm the display order. PTL 1, for example, proposes a scheme for selecting pictures output from a decoder on the basis of a reproduction speed.